ASHRAE Standard 55 specifies conditions for acceptable thermal environments and is intended for use in design, operation, and commissioning of buildings and other occupied spaces.

The 2020 edition of ANSI/ASHRAE Standard 55 incorporates eight published addenda to the 2017 edition. This version steers users toward the analytical method (and companion elevated airspeed method) and replaces the graphical method with a series of examples that use the analytical method. With multiple freely available third-party implementations of the analytical method, barriers to its use have been greatly reduced, allowing for greater flexibility and accuracy than with the graphical method.

The standard includes a separate adaptive model for determining acceptable thermal conditions in occupant-controlled naturally conditioned spaces, with newly expanded applicability in this version. Users are now allowed to use the adaptive model when an air-conditioning unit is installed but not operating.

Other noteworthy additions to the standard include the addition of a new method for the avoidance of draft risk at the ankle region, as well as new Thermal Environmental Control Classification Levels that document how much control an occupant has over their thermal environment. These levels were added to Section 6 of the standard and are required elements of documenting compliance with Standard 55.